The present invention generally relates to new and useful improvements in closure caps for glass and plastic containers and, more particularly, to a closure cap having an improved injection molded annular gasket and method of making the same. In this regard, an important aspect of the present invention is directed to a closure cap having a one-piece or unitary cap shell formed of a polyolefin such as, for example, polypropylene, in which an annular or ring-shaped gasket characterized by improved uniformity, definition and consistency which is composed of a moldable resin such as, for example, a thermoplastic elastomer, is injection molded onto the inner surface of the closure cap shell via an insert molding procedure.
Closure caps having full disks formed by compression or injection molding the same in a closure shell are known. For example, U.S. Pat. No. 4,398,874 describes a molding tool for forming a full disk liner in a closure shell which includes a central punch or molding member and a shell positioning sleeve disposed externally of the molding member that is received within a cap shell. Liner material deposited within the shell is contacted by the punch and forms a full disk liner with the cap shell. Correspondingly, U.S. Pat. No. 4,803,031 describes a closure cap and method wherein an injection molded full disk gasket is formed followed by injection molding the closure cap shell around the thus formed gasket. These full disk closure caps while providing generally satisfactory sealing on containers are characterized by higher manufacturing costs associated with using greater amounts of gasket-forming resin and also by the disadvantages of having the entire inside surface of the cap shell fully covered thereby increasing the possible migration of gasket components into product (particularly food products) in the container sealed therewith and also making the inner surface of the cap shell unavailable for displaying labels or other message-conveying indicia.
U.S. Pat. No. 5,685,443 describes a composite closure cap where an annular gasket providing a top and side seal is injection molded onto a metal disk followed by injection molding a plastic skirt around the disk in surrounding and capturing relation therewith. This composite closure while utilizing an injection molded annular gasket requires the presence of a separate disk which adds to the cost of the closure and to the complexity of manufacturing the same.